I've long opened everything in a new tab, but would you believe I just realised I need to consciously make the effort to open new "projects" in new windows 2 hours before reading this post? I think the difficulty is working out when that line of a tangent has been crossed.

Tree-style tabs [0] in Firefox help to keep a train of "research" together.

[0]: https://addons.mozilla.org/en-US/firefox/addon/tree-style-ta...